In recent years, flat panel display devices that use flat panel display elements such as liquid crystal panels and plasma display panels are increasingly used as display elements for image display devices such as television receivers instead of conventional cathode-ray tube displays, allowing image display devices to be made thinner. Liquid crystal panels used in liquid crystal display devices do not emit light on their own, and therefore, it is necessary to provide a separate backlight device as an illumination device.
An example of a conventional backlight device is an edge light-type backlight device in which a light-receiving surface is provided on a side face of a light guide plate, and a light source such as an LED is provided at the side face of the light guide plate. In such a backlight device, in order to enhance the utilization efficiency of light that entered the light guide plate, a reflective sheet is sometimes provided in a chassis, in addition to the light guide plate and the light source. The reflective sheet that reflects light is provided on a plate surface of the light guide plate on a side opposite to the light-emitting surface.
In the backlight device in which a reflective sheet that reflects light is provided on the plate surface of the light guide plate on the side opposite to the light-emitting surface in the chassis, if an edge of the reflective sheet on the side facing the light source is located further back from a surface of the light guide plate facing the light source, a bright line can appear on the display surface in a position overlapping the face of the light guide plate that faces the light source, possibly causing a display defect. In order to solve this problem, a technique is known in which the edge of the reflective sheet on the side facing the light source is extended toward the light source beyond the surface of the light guide plate facing the light source in the backlight device, thereby preventing the occurrence of the bright line. Patent Document 1 discloses such a backlight device, for example.